1. Field of the Invention
The field of the present invention relates to estimating engine operating parameters of an internal combustion engine of a vehicle. More particularly, the present invention relates to a method for estimating manifold pressure of an engine having numerous actuators that affect engine breathing, such as a charge motion control valve, valve timing actuators and valve lift actuators.
2. Background of the Invention
Various methods can be used to estimate operating parameters of a vehicle""s internal combustion engine. One particular parameter that is estimated using information from vehicle sensors is manifold pressure. An example approach is described in U.S. Pat. No. 5,331,936.
The inventors herein have recognized a disadvantage with this and other prior art systems. As new engine actuators are continually added, the complexity in estimating manifold pressure (and other operating parameters) grows exponentially. For example, in engines that have both adjustable intake and exhaust valve timing, the complexity of estimating manifold pressure can be overbearing, especially during dynamic situations. In other words, manifold pressure is dependent on intake cam opening time, intake cam closing time, exhaust valve opening time, exhaust valve closing time, engine speed, mass air flow, barometric pressure, engine temperatures, etc. To map the engine at every possible combination becomes a difficult and expensive task.
The above disadvantages are overcome by a method for controlling an engine of a vehicle, the engine having a variable valve actuator. The method comprises:
storing manifold pressure related parameters [slope and offset parameters] as a function of intake and exhaust valve timing at a subset of engine operating conditions, said subset including at least a default operating point, and a predetermined set of normal conditions, and an intermediate point away from normal operating conditions;
calculating current manifold pressure related parameters based on actual engine speed and actual intake and exhaust valve timings using said stored manifold pressure related parameters;
estimating an engine state based on said current manifold pressure related parameters, and based on at least one engine operating condition;
controlling the engine based on said estimated engine state.
By storing data as a function of intake and exhaust valve timing, with the data indexed by a default operating point, a predetermined set of normal conditions, and an intermediate point, it is possible to accurately cover real world operating conditions of the engine. In other words, data storage is a fraction of that used with prior art approaches, which also results in algorithm simplification. As such, it is possible to accommodate a great number of engine actuators that affect engine state estimation without continually expanding data storage and algorithm calculations at an exponential rate.
Further, by providing an accurate and efficient method to estimate manifold pressure, it is possible to develop advanced engine technologies including variable intake and exhaust timing, while still eliminating the cost of a manifold pressure sensor.